Fluoride ion emission, shear bond strength, and adhesive remnant index of calcium fluoride nanoparticles-containing orthodontic primer: an <i>In Vitro</i> study

Abstract Objectives This study investigated fluoride ion emission, shear bond strength (SBS), and the adhesive remnant index (ARI) of orthodontic primers containing varying percentages of calcium fluoride nanoparticles (nCaF 2 ). Methods Four primers were prepared with nCaF 2 concentrations of 0%, 20%, 30%, and 40%, mixed with Transbond XT primer (3M-Unitek, Monrovia, USA). Twenty-eight extracted upper premolars were equally divided into four groups, and bonded with orthodontic brackets using the respective primers following a standardised protocol. Fluoride ion emission was measured daily for two weeks, followed by assessments of SBS and ARI. Results The mean fluoride ion released was significantly different between the four groups. All groups showed higher initial fluoride ion levels, which later stabilised. Notably, only the primers with 40% nCaF 2 consistently released fluoride ions above 0.010 ppm, reaching 0.014 ppm on most days and stabilising between 0.011 and 0.026 ppm from Day 6 to Day 14. SBS differed significantly between the groups [ F (3,24)=4.977, p =0.008], with the 40% nCaF 2 group showing significantly reduced SBS, although not to a clinically significant extent. ARI was unaffected [χ 2(2, N = 28) = 3.589, p = 0.263]. Conclusions Orthodontic primers with 40% nCaF 2 maintained fluoride ion release levels that may be clinically effective in combating white spot lesions, without compromising the SBS and ARI.